Low temperature separation process of normally gaseous materials by plural stage phase separations



A nl 28, 1970 J. A. PRYOR 3,508,413

LOW TEMPERATURE SEPARATION PROCESS OF NORMALLY GASEOUS MATERIALS BYPLURAL STAGE PHASE SEPARATIONS Original Filed Nov. 22, 1965 3Sheets-Sheet 1 SUBATMOSPHERIC PRESSURE INVENTOR.

JOHN A. PRYOR BY Smiwsw A TTORNE Y A ril 28, 1970 J. A. PRYOR LOWTEMPERATURE SEPARATION PROCESS OF NORMALLY 'GASEOUS MATERIALS BY PLURALSTAGE PHASE SEPARATIONS 5 Sheets-Sheet 2 Original Filed Nov. 22. 1965umnwmwza uiurawoihqmam INVENTOR.

JOHN A. PRYOR ATTORNEY April 28, 1970 J. A. PR-YOR 3,508,413

' LOW TEMPERATURE SEPARATION PROCESS OFv-NORMALLY GASEOUS MATERIALS BYPLURAL STAGE PHASE SEPARATIONS Origlnal Filed Nov. 22, 1965 3Sheets-Sheet 5 INVENTOR JOHN A. PRYOR MS QM ATTORNEYS United StatesPatent Office 3,508,413 Patented Apr. 28, 1970 Int. Cl. F25j 3/02 U.S.CI. 62-24 8 Claims ABSTRACT OF THE DISCLOSURE Low temperature processfor separation of a gaseous mixture into components. A gaseous mixturecontaining components of different boiling points is compressed, cooledand passed through a sequence of liquefaction and separation steps incycles characterized by high thermal efiiciency and low powerrequirements, to effect separation of the mixture into streams rich inthe respective components.

This is a division of copending application Ser. No. 513,648, filed Nov.22, 1965, now U.S. Patent No. 3,319,- 429, May 16, 1967, which is acontinuation-in-part of copending application Ser. No. 274,489, filedApr. 22, 1963, now abandoned.

The present invention relates to methods for separating the componentsof mixtures of normally gaseous materials, and more particularly, tomethods for low temperature liquefaction and fractionation of mixturesof normally gaseous materials.

An object of the present invention is to provide methods for separatingmixtures of normally gaseous materials, which are characterized by highthermal efliciency.

Another object of the present invention is the provision of methods forseparating normally gaseous mixtures, which are characterized byrelatively low power requirements.

Still another object of the present invention is the provision ofmethods for separating mixtures of hydrogen and carbon monoxide.

A further object of the present invention is the provision of methodsfor separating ternary gaseous mixtures.

Still anotherobject of the present invention is the provision of methodsfor separating mixtures comprising hydrogen, carbon monoxide andmethane.

Yet another object of the present invention is to provide improved lowtemperature methods for separating gaseous mixtures, in which part ofthe refrigeration required is supplied by evaporating a liquid, normallygaseous refrigerant under subatmospheric pressure.

Still a further object of the present invention is to provide improvedmethods for separating gaseous mixtures which will be relatively simple,reliable and inexpensive in practice.

The foregoing and other objects are accomplished by the invention, whichin one embodiment can be briefly described as a low temperature processfor separating components of a mixture including a relatively lowerboiling, normally gaseous first component, a relatively intermediateboiling, normally gaseous second component and a relatively higherboiling, normally gaseous third component, comprising the steps ofcooling and partially condensing compressed mixture to form a vapor richin first component and a condensate rich in second component andcontaining third component, separating vapor rich in first componentfrom condensate, passing at least a portion of the condensate to anevaporation zone, maintaining condensate in the evaporation zone undersubatmospheric pressure, passing compressed mixture in heat exchangerelationship with condensate in the separation zone to assist in coolingand partially condensing mixture, thereby partially vaporizingcondensate under subatmospheric pressure to obtain a vapor rich insecond component, and withdrawing vaporized condensate rich in secondcomponent to leave a liquid residue containing third component.

In another embodiment, the invention may be briefly described as a lowtemperature process for separating components of a mixture including arelatively lower boiling; normally gaseous first component and arelatively higher boiling, normally gaseous second component, comprisingthe steps of compressing and expanding a normally gaseous refrigerant ina closed cycle in which the refrigerant is compressed to asuperatmospheric pressure, cooled to effect at least partialliquefaction thereof, and expanded to a subatmospheric pressure,compressing and cooling mixture, passing cooled, compressed mixture inheat exchange relationship with refrigerant evaporating undersubatmospheric pressure to effect further cooling and at least partialcondensation of mixture to form a vapor rich in first component and acondensate rich in second component, and separating vapor rich in firstcomponent from condensate rich in second component.

Other features, objects and advantages of the invention will appear morefully from the following detailed description which, when considered inconnection'with the accompanying drawings, discloses several embodimentsof the invention for purposes of illustration only and not fordefinition of the limits of the invention. For determining the scope ofthe invention, reference may be had to the appended claims.

In the drawings, wherein similar reference characters denote similarelements throughout the several views;

FIGURE 1 is a diagrammatic showing of a low temperature gas separationprocess that forms a preferred embodiment of the present invention.

FIGURE 2 is a partial diagrammatic showing of a modified form of theembodiment shown in FIGURE 1; and

FIGURE 3 is a diagrammatic showing of a low temperature gas separationprocess that forms another embodiment of the invention.

Referring now to the drawings in greater detail, in FIGURE 1, acompressed feed gas mixture enters the system at a relatively highpressure through a conduit 1 and is divided and passes through a pair ofbranch conduits 3 and 5, which are in parallel with each other. Themixture in conduit 3 is cooled in heat exchanger 7 by returning gasstreams, while the mixture in conduit 5 is similarly cooled in heatexchanger 9. The streams in conduits 3 and 5 are then merged in conduit11 and are passed through the reboiler 13 of a fractionating column 15in which they are further cooled and partially condensed. Column 15 hasthe usual rectification trays 17.

The partially condensed mixture is then passed to a phase separator 19,in which a liquid fraction is separated from a remaining vapor fraction.The liquid fraction is removed through a conduit and is expanded throughexpansion valve 23 in which a vapor is flashed off the liquid. The mixedliquid and vapor are then introduced into a phase separator 25 in whicha body of liquid and a body of vapor collect and are separately.

removed. The liquid is removed through a conduit 27, and a vapor isflashed off in an expansion valve 29. The mixed liquid and vapor areintroduced at the appropriate composition level into fractionatingcolumn 15. The vapor from phase separator 25 is removed through aconduit 31, warmed by passage through heat exchanger 9 in heat exchangerelationship with entering feed gas in branch conduit 5, compressed inrecycle compressor 33 and reintroduced into conduit 1 for recycle withthe feed gas.

Returning now to phase separator 19, the remaining vapor fraction of thefeed mixture is removed from phase separator 19 through a conduit 35 andis further cooled and partially condensed in the heat exchanger 37. Thepartially condensed material is then introduced into a phase separator39 and is separated into vapor and liquid phases. The liquid phase isremoved through conduit 41 and a vapor is flashed from it throughexpansion valve 43, after which the mixed liquid and vapor join themixed liquid and vapor in conduit 21 on the way toward phase separator25.

The vapor from phase separator 39 is withdrawn through a conduit 45.andis returned to heat exchanger 37, where it is further cooled andpartially condensed, to emerge from the exchanger 37 and be passedthrough a .coil 47 in the base of an evaporator 49. The mixture inconduit 45 is further partially condensed in coil 47 and is fed into aphase separator 51, in which it is separated into liquid condensate andvapor portions. The vapor portion, rich in relatively lower boilingfirst component of the mixture, is withdrawn, through conduit 53, warmedby passage through exchanger 37, cooled by expansion with production ofexternal work in expansion engine 55, and introduced into the shell sideof exchanger 37, where it serves to cool incoming gas mixture. The vaporportion is then removed through a conduit 57, passed to the shell sideof exchanger 7, withdrawn from exchanger 7 and compressed in acompressor 59. The product emerging from compressor 59'is recovered asthe relatively lower boiling component of the mixture. That is to say,this component has the lower boiling point of the major components ofthe mixture.

Returning now to phase separator 51, the condensate, rich in relativelyintermediate boiling, second component and containing relatively higherboiling third component, is removed from phase separator 51 to a conduit61, passed from the cold end through to the warm end of exchanger 37 andis expanded through an expansion valve 63 in which further vapor rich inrelatively lower boiling component is flashed from the liquid. The mixedliquid and vapor are introduced into a phase separator 65, in which thevapor and liquid are separated from each other, the vapor beingwithdrawn through conduit 67 and merged in conduit 31 for recycling withthe vapor from phase separator 25. The liquid from phase separator 65 isexpanded through expansion valve 75 and a vapor flashed therefrom, andthe mixed liquid and vapor are introduced into evaporator 49, in which abody of liquid 77 is collected and maintained under subatmosphericpressure. Most of the liquid in the evaporator 49 is evaporated undersubatmospheric pressure and withdrawn as vapor, rich in relativelyintermediate boiling second component, through a conduit 83 andintroduced into the cold end of heat exchanger 9, through which itpasses on the shell side of the exchanger to be removed at the warm endof the exchanger and introduced into the low pressure stage of acompressor 85. Liquid residue, containing relatively higher boilingthird component, is bled from evaporator 49 through a conduit 79 pumpedto higher pressure in a pump 81 and introduced at its appropriatecomposition level in fractionating column 15.

The vapor overhead from fractionating column 15, also rich in relativelyintermediate boiling second component, is Withdrawn at superatmosphericpressure through a conduit 87 and passed through a separate passagewayin heat exchanger 7 from the cold to the warm end thereof, to be thenintroduced into the intermediate pressure stage of compressor 85. Thematerial in conduits 83 and 87 thus becomes intermingled and is raisedto relatively high pressure, and emerges through a con- 4. duit 89 to berecovered as product, the relatively intermediate boiling, secondcomponent of the mixture.

The liquid bottoms from fractionating column'15, enriched in relativelyhigher boiling, third component of the mixture, are removed through aconduit 91, passed from the cold end to the warm end of exchanger 9 tocool the entering feed, compressed in compressor 93 and removed as purgegas, enriched in the relatively higher boiling product of the separationprocess.

very important feature of this embodiment of the invention is theprovision of evaporator 49 maintained at subatmospheric pressure. Thepressure downstream of expansion valve and upstream of the low pressurestage of compressor '85, in conduit 83, is thus subatmospheric, and thefeed to evaporator 49, in conduit 69, is thus flashed to subatmosphericpressure and evaporation or ,boil-up from boil 47 is also conducted atsubatmospheric pressure.

It has been found that evaporation at subatmospheric pressure greatlyincreases the thermal efliciency of the cycle and therefore greatlyreduces the power requirements of the process. As a result of thusevaporating the liquid at subatmospheric pressure, the liquid isevaporated at a lower temperature than that at which it condensed. Thetemperature difference between the various streams at the warm and coldends of the heat exchangers 7 and 9 is reduced, thus making the cyclemore thermodynamically reversible and thus reducing the refrigerationload on the cycle.

The following is a specific example of operation according to theembodiment of FIGURE 1:

Feed gas enters the' cycle through conduit 1 at a pressure of 617p.s.i.a. and 40 F. with a composition of 88.68% hydrogen, 10.78% CO and0.54% methane, which includes the recycle stream through conduit 31. Thefeed gas stream is divided and passed in parallel through exchangers 7and 9 and recombined in conduit 11 with a temperature of 292 F. Afterpassage through the reboiler 13, the temperature is 299 F.

The liquid fraction separated in phase separator 19 has a composition of8.81% hydrogen, 76.65% CO and 14.54% methane. It has a temperature of299 F. and is at a pressure of 606 p.s.i.a. It is expanded through valve23 to a temperature of -303 F. and a pressure of p.s.i.a. and introducedinto phase separator 25, in which there separates out a liquidcontaining 1.06% hydrogen, 85.66% carbon monoxide and 13.28% methane.This latter liquid is expanded through valve 29 from a pressure of 80p.s.i.a. to a pressure of 19 p.s.i.a. and a temperature of 306 F. and isintroduced in this condition into fractionating column 15. The vaporfrom phase separator 25 is recycled through conduit 31 and has atemperature of 06 F., a pressure of 80 p.s.i.a., and a composition of66.82% hydrogen, 32.99% CO and 0.19% methane.

Returning to phase separator 19, the remaining fraction of the feedmixture leaves this separator at 606 p.s.i.a. and 299 F., and has acomposition of 90.62% hydrogen, 9.18% CO and 0.20% methane. It is cooledin the warm end of heat exchanger 37 to a temperature of 305 F. and apressure of 604 p.s.i.a., partially condensed, and introduced into phaseseparator 39, in which there separates out a liquid that is removedthrough conduit 41 at -305 F. and 604 p.s.i.a., with a composition of8.36% hydrogen, 83.76% CO and 7.88% methane. This liquid is expandedthrough valve 43 to a temperature of -309 F. and a pressure of 80p.s.i.a. and is added to the material in conduit 21 on the way to phaseseparator 25.

The overhead from separator 39 has a temperature of 305 F., a pressureof 604 p.s.i.a., and a composition of 91.98% hydrogen, 7.95% CO and 0.7%methane. It is reintroduced into exchanger 37 and is cooled in thatexchanger to a temperature of -322.2 F. at a pressure of 601 p.s.i.a.,and partially condensed. In this.

condition, the mixture passes through coil 47, in which it is cooled to330.5 F. and a pressure of 595 p.s.i.a., further partially condensed,and passed into phase separator 51. The vapor phase, at that sametemperature, has a composition of 97.5% hydrogen and 2.5% carbonmonoxide and is suitable for use as product hydrogen. It is removed fromseparator 51, expanded in expansion engine 55 to a pressure of 290p.s.i.a. and a temperature of 333 F., warmed in exchanger 37 to atemperature of -304 F., and again in exchanger 7 to a temperature of 35F. It is then compressed in compressor 59 to a pressure of 595 p.s.i.a.and has a temperature, following passage through the usual compressoraftercoolers, of 100 F., in which condition it is recovered as producthydrogen, the relatively lower boiling, normally gaseous first componentof the mixture.

The condensate leaving phase separator 51 is at 330.5 F. and 595p.s.i.a. and has a composition that is 6.94% hydrogen, 91.86% carbonmonoxide and 1.20% methane. It is warmed in exchanger 37 to atemperature of 304 F., and is expanded in expansion valve 63 from 592p.s.i.a. to 50 p.s.i.a., during the course of which it falls intemperature to 309 F. and leaves expansion valve 63 partly in liquidphase and partly in vapor phase. The vapor phase material that isseparated in phase separator 65 has a temperature of 304 F., and apressure of 50 p.s.i.a., and a composition that is 64.88% hydrogen,35.11% carbon monoxide and 0.01% methane, and joins the recycle streamin conduit 31. The liquid from phase separator 65 leaves through conduit69 at a temperature of 309 F. and a pressure of 50 p.s.i.a. and has acomposition that is 1.03% hydrogen, 97.65% carbon monoxide and 1.32%methane. It is expanded in valve 75 to a pressure of 3.0 p.s.i.a. and atemperature of 333 F. in which condition it is partly in liquid andpartly in vapor phase.

Another branch of the liquid from phase separator 65 is expanded throughvalve 73 from 49 p.s.i.a. to 18.5 p.s.i.a. and is introduced into thetop of fractionating column 15 as liquid reflux.

The material in line 69 is then introduced into evaporator 49, and theliquid residue that is bled from the bottom of evaporator 49 is at 331.5F. and 2.0 p.s.i.a. and has a composition that is 92.65% CO and 7.35%methane. This material is raised in pressure in pump 81 to 18.8 p.s.i.a.and a temperature of 330 F., and is introduced into column 15 at itsappropriate composition level.

The vaporized condensate leaving evaporator 49 is at a temperature of330.5 F. and a subatmospheric pressure of 2.8 p.s.i.a. and has acomposition that is 1.00% hydrogen, 98.90% carbon monoxide and 0.10%methane. This vapor is then warmed in exchanger 9 to a temperature of 28F. and is compressed in the low 'pressure stage of compressor 85. Theoverheads withdrawn from fractionating column 15 in conduit 87 are at atemperature of -310 F. and a superatmospheric pressure of 18.5 p.s.i.a.and have the same composition as the material in conduit 83. Theoverheads are warmed in exchanger 7 to a temperature of 28 F. at apressure of 15.5 p.s.i.a. in which condition they enter the intermediatestage of compressor 85. The material finally leaving compressor 85through conduit 89 is at a pressure of 310 p.s.i.a. and has atemperature of 100 F., allowing .for aftercooling, and is recovered asproduct carbon monoxide, the relatively intermediate boiling, normallygaseous second component of the mixture. The material leaving the bottomof fractionating column 15 thlOPgh conduit 91 is in liquid phase and hasa pressure of 20 p.s.i.a., a temperature of 302.3 F., and a compositionof 60% CO and 40% methane. This material is warmed and vaporized inexchanger 9 to 28 F., compressed in compressor 93 to a pressure of 225p.s.i.a. and a temperature of 100 F., and vented from the system,enriched in methane, the relatively higher boiling, normally gaseousthird component of the mixture.

Turning now to FIGURE 2, it will be seen that a modification of theembodiment of FIGURE 1 has been made, in which the liquid from phaseseparator 39 passes through conduit and is expanded through expansionvalve 97 from 604 p.s.i.a. to 80 p.s.i.a. whereby a vapor is flashedfrom the liquid. The mixed liquid and vapor is introduced into a phaseseparator 99 from which the liquid leaves through conduit 101 and isexpanded through valve 103 from 80 p.s.i.a. to 2.8 p.s.i.a. so that avapor is flashed in valve 103 and the mixed liquid and vapor isintroduced into a fractionating column 105 at the appropriatecomposition level. Column 105 is provided with appropriate fractionatingtrays 107. Vapor from phase separator 99 leaves through conduit 109 andjoins the vapor in conduit 31. Otherwise, the structure and operation ofthe cycle of FIGURE 2 are substantially the same as the structure andfunction of the cylce of FIGURE 1, it being noted that the use either ofan evaporator 49 or of a fractionating column 105 as the subatmosphericevaporation zone is within the scope of the present invention.

With respect to the embodiment shown in FIGURE 3, feed has mixtureenters the system through a conduit 118 and passes into compressor 119,from which it emerges at elevated pressure to pass through conduit 120to chiller 122, where it is cooled. The feed gas then passes via conduit123 to enter one of two alternately operable driers 124, arranged toallow continuous operation of the process. Thus, one drier will be inoperation while the other is out of service for reactivation. Suitablevalve means 126 are provided to permit switching of the feed gas steramfrom one drier to the other. After leaving a drier 124, the feed gascontinues through conduit 128 to begin its first pass through heatexchanger 130 to be cooled by returning gas streams. At a pointintermediate its pass through exchanger 130, the feed gas is withdrawnthrough conduit 132 and passed through one of two parallel, alternatelyoperable carbon dioxide adsorbers 134. Suitable valve means 136 areprovided to permit alternate operation of the CO adsorbers in a fashionsimilar to that of the driers 124, so that one adsorber can be taken outof service for reactivation without interrupting the process. After COis removed from the feed gas, the stream is returned via conduit 138 tofinish its pass through heat exchanger 130.

The feed gas stream leaves the coldend of exchanger 130 by way ofconduit 140 and is divided at point 141. One branch of the split feedstream passes through conduit 142 and is further cooled by acting asreboiler in coil.143 in phase separator 144. This branch emerges fromseparator 144 by way of conduit 146. The other branch continues fromdivision point 141 on through conduit148 to be further cooled by actingas reboiler in coil 149 in phase separator 150. This latter branch exitsseparator 150 in conduit 152 to rejoin the other branch stream at point154.

The feed gas continues from point 154 on through conduit 156 and coil157 to reboil liquid in the bottom of fractionating column 158, and isfurther cooled and partially condensed in the process. Column 158 hasthe usual rectification trays 155. Partially condensed feed gas mixturepasses from column 158 through conduit 159 into phase separator 160where a liquid fraction is separated from a remaining vapor fraction.The remaining vapor fraction from separator 160 passes through conduit162 and enters heat exchanger 164 for further cooling and partialcondensation. Intermediate its passage through exchanger 164, themixture is extracted via conduit 166 to pass to coil 167, to reboil andbe cooled by liquid refrigerant in evaporator 168. The gas mixtureemerges from evaporator 168 and passes through conduit 170 to return toexchanger 164 to complete its pass.

The partially condensed mixture leaves exchanger 164 through conduit 172and passes into coil 173 in refrigerant evaporator 174, where liquidrefrigerant boiling under subatmospheric pressure effects furtherpartial condensation of the mixture. From evaporator 174, the mixture inmixed-phase stream, passes via conduit 176 to phase separator 178. Thevapor phase, rich in relatively lower boiling, normally gaseous firstcomponent, passes from phase separator 178 through conduit 180 toexchanger 164 where it serves to cool incoming gas, to emerge viaconduit 182 and pass through exchanger 130 to assist in cooling enteringfeed gas. This vapor stream exists exchanger 130 through conduit 184 andis recovered as the relatively lower boiling, normally gaseous firstcomponent of the mixture.

Condensate remaining in separator 178 rich in relatively higher boiling,normally gaseous second component and also containing relatively stillhigher boiling, normally gaseous third component drains through conduit186 to pass through exchanger 164, to emerge through conduit 188 to bepassed through expansion valve 189 in which a further vapor rich inrelatively lower boiling first component is flashed from the liquid withboth phases being passed into separator 144.

Liquid bottoms from separator 160 are passed by way of conduit 190 andare flashed across valve 191 to form a mixed-phase stream which passesinto separator 150. Vapors from separators 144 and 150 enriched inrelatively lower boiling first component, exit through conduits 192 and194 respectively to merge in conduit 196 and pass through exchanger 130to serve to cool incoming feed gas. The vapor stream from conduit 196exits exchanger 130 through conduit 198 and passes as recycle gasthrough recycle compressor 200 to rejoin the feed stream in conduit 120at point 202.

The liquid bottoms from separator 144 are drained through conduit 204and are divided at point 205, part passing through conduit 206 to act asreflux in fractionating column 158, and the remainder continuing throughconduit 207 to be flashed across valve 208 and passed into phaseseparator 209. The liquid bottoms from sepa' rator 150 pass throughconduit 151 are flashed across valve 210 and also enter separator 209.

Liquid bottoms from separator 209 drain through conduit 211 into coil213 of refrigerant condenser 212 from where, after liquefyingrefrigerant, they return to separator 209 via conduit 214. Liquidbottoms from separator 209 also pass via conduit 215 into fractionatingcolumn 158 at an appropriate composition level. Thus, the overheads andthe liquid bottoms from separator 209 both flow into the column 158, butat different locations.

The liquid at the bottom of fractionating column 158 is reboiled by thefeed gas mixture passing through coil 157. Overheads from column 158rich in relatively higher boiling, second component are withdrawn atsuperatmospheric pressure and pass through conduit 216 to exchanger 130,thereby serving to cool incoming gases. These overheads are withdrawnfrom the system through conduit 218 as the relatively higher boiling,normally gaseous second component of the mixture, and are recovered as aproduct of the fractionation.

Liquid bottoms in fractionating column 158 are drained through conduit220 and are passed to exchanger 130, whereby they serve to cool incomingfeed gas mixture, and are vaporized in the process. This vapor emergesfrom exchanger 130 by way of conduit 222 as a stream enriched in therelatively still higher boiling, third component of the mixture. Thisstream is divided at point 223, a portion being vented from the systemas purge gas through conduit 224 and another portion being passedthrough conduit 225 into compressor 226. This latter portion, underelevated pressure is passed through conduit 227 to be chilled inrefrigerator 228. From refrigerator 228, the gas passes through conduit229 into phase separator 230. The overheads from this separator passthrough conduit 231 and are returned to fractionating column 158 forreclamation. The liquid bottoms drain through conduit 232, rejoin theliquid bottoms from fractionating column 158 at point 233 and pass outthrough the exchanger 130.

'In this embodiment of the invention, the refrigeration system whichcools the feed gas in the evaporators is a closed cycle. The refrigerantis compressed in compressor 240 to a first superatmospheric pressure,passes through conduit 241 into suitable oil filtering apparatus 242 andthrough conduit 243 into exchanger 244, where it is cooled by heatinterchange with returning refrigerant streams. From exchanger 244, therefrigerant passes by Way of conduit 246 into coil 247 in therefrigerant condenser 212 where it is liquefied by heat exchange withliquid bottoms from separator 209. The refrigerant emerges. from therefrigerant condenser 212 through conduit 248 and passes intorefrigerant subcooling coil 250 in refrigerant evaporator 168. In coil250, the refrigerant is subcooled by refrigerant vaporized in evaporator168. The refrigerant from coil 250 is flashed across valve 251 to asecond superatmospheric pressure and passes into evaporator 168 in thatcondition. The refrigerant that is vaporized emerges through conduit 252into exchanger 244 and returns to the suction side of compressor 240 byway of conduit 254.

Liquid refrigerant in evaporator 168 flows through conduit 256 intorefrigerant subcooling coil 258, where it is subcooled by refrigerantvaporized under subatmospheric pressure in evaporator 174. The liquidfrom coil 258 is flashed across valve 259 to a subatmospheric pressureand passes into refrigerant evaporator 174, where it is maintained undersubatmospheric pressure. In evaporator 174, the refrigerant is vaporizedunder subatmospheric'pressure, thereby serving to cool incoming gasmixture in coil 173, to effect partial condensation thereof. Thevaporized refrigerant passes out of evaporator 174, subcooling incomingrefrigerant in coil 258 en route, and exits through conduit 260, to passthrough refrigerant exchanger 244. From refrigerant exchanger 244, thereturning refrigerant passes through refrigerant vacuum pump 261 to jointhe refrigerant recycle stream in conduit 254 and return to therefrigerant compressor 240.

As a specific operating example of the embodiment of the inventionaccording to FIGURE 3, feed gas mixture comprising, by volume, about 65%hydrogen, 34% carbon monoxide, 0.6% methane and the balance traceconstituents, enters the system and is compressed to about 455 p.s.i.a.leaving compressor 119 at about F. The rate of flow is about 1729pound-mols per hours on a dry basis (14.90 MMSCFD). The feed gas thenpasses through ammonia chiller 122 to be cooled to about 35 F. The feedstream passes into exchanger and is withdrawn therefrom through conduit132 at about 115 F. for removal of C0 The feed gas finishes its passthrough exchanger 130, to exit therefrom through conduit and passthrough coil 157 in fractionation column 158, emerging at '-284 F. toenter the phase separator 160 at that temperature. The overheads fromseparator 160 pass to exchanger 164 for further cooling and partialliquefaction, are withdrawn through conduit 166 to pass through liquidnitrogen evaporator 168 and be cooled by liquid nitrogen which isvaporizing at 22 p.s.i.a.

The mixture re-enters exchanger 164 through conduit 170, emerges throughconduit 172 and passes into coil 173 in evaporator 174, where it iscooled by liquid nitrogen boiling at a pressure of about 4.6 p.s.i.a.The feed stream having undergone further partial condensation in coil173, is then passed into separator 178, which it enters at a pressure ofabout 440 p.s.i.a. and a temperature of about 334 F. Vapor rich inhydrogen (98.45% hydrogen, 1.50% carbon monoxide, balance traceelements) is passed out through conduit 180 to pass through exchanger130, emerging at a temperature of about 30 F. and a pressure of about415 p.s.i.a. to be recovered as product hydrogen.

The overheads from fractionating column 158, vapors rich in carbonmonoxide (98.6% carbon monoxide, 0.1% hydrogen, 0.1% methane, balancetrace elements), are removed from column 158 at a pressure of about 19p.s.i.a. and a temperature of about -310 F. Those vapors are passed byway of conduit 216 out through exchanger 130, emerging therefrom at atemperature of about 30 F. and a pressure of about 16 p.s.i.a. to berecovered as product carbon monoxide.

Liquid bottoms from fractionating column 158 are withdrawn as a purgestream through exchanger 130, emerging as a vaporized stream at atemperature of about 30 F., that is divided at point 223, with aboutone-third being vented from the system through conduit 224, and abouttwo-thirds continuing on as recycle. The purge stream has a compositionof about 70% methane and 30% carbon monoxide, with traces of otherconstituents. The recycle purge stream is compressed in compressor 226to about 1050 p.s.i.a., leaving at a temperature of about 96 F. to becooled in ammonia chillers 228 to a temperature of about 1'20 F. Therecycle purge gas is flashed to about 19 p.s.i.a. in separator 230, fromwhich the overheads and bottoms pass to their respective locations inthe system as set forth hereinabove.

The overheads leaving the tops of separators 144 and 150 emerge at apressure of about 75 p.s.i.a., pass through exchanger 130 to exittherefrom at a temperature of about 30 F., are compressed in recyclecompressor 200 to about 455 p.s.i.a. at a temperature of 86 F., in whichcondition they rejoin the feed stream in conduit 120.

The normally gaseous refrigerant, in this case nitrogen, is compressedin compressor 240 to a first superatmospheric pressure of about 45p.s.i.a. at a temperature of about 100 F., and enters exchanger 244 inthis condition. The nitrogen is liquefied in condenser 212, subcooled incooling coil 250, and is flashed across valve 251 to enter evaporator168 at a second superatmospheric pressure of about 22 p.s.i.a., at whichpressure some of the liquid nitrogen is vaporized by the mixture in coil167.

Liquid nitrogen drains from evaporator 168 to be further subcooled incoil 258, and flashed across valve 259 to enter evaporator 174 at asubatmospheric pressure of about 4.6 p.s.i.a. Vaporized nitrogen passingout of evaporator 174 returns through exchanger 244 and nitrogen vacuumpump 261, to rejoin the other returning nitrogen stream, both of whichreturn to compressor 240 at about 16 p.s.i.a.

Although the present invention has been described and illustrated inconnection with preferred embodiments, it is to be understood thatmodifications and variations may be resorted to without departing fromthe spirit of the invention, as those skilled in this art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the present invention as defined by theappended claims.

What I claim is:

1. Low temperature process for separating components of a gaseousmixture including a first component of relatively low boiling point, asecond component of next lower boiling point and a third component ofrelatively higher boiling point, comprising the steps of compressing thegaseous mixture,

cooling compressed gaseous mixture by heat interchange with relativelycold components of the gaseous mixture to effect partial liquefaction ofthe gaseous mixture and provide a first vapor and a first condensate,separating the first vapor from the first condensate,

cooling the first vapor without rectification, by heat interchange witha relatively cold extraneous refrigerant to effect its partialliquefaction and provide a second vapor consisting essentially of thefirst component and a second condensate,

separating the second vapor from the second condensate,

warming and expanding and partially evaporating the second condensate toproduce a third vapor and a third condensate, separating the third vaporfrom the third condensate, introducing third condensate into afractionating zone and separating third condensate into a fourth vaporconsisting essentially of the second component and a fourth condensate,collecting in the zone,

and passing the second vapor and the fourth vapor in heat interchangewith the compressed gaseous mixture to effect at least part of thecooling of the compressed gaseous mixture.

2. Low temperature process as defined in claim 1 in which the extraneousrefrigerant comprises a liquefied gas under subatmospheric pressure.

3. Low temperature process as defined in claim 1 in which the firstcondensate is expanded, partly evaporated and then introduced into thefractionating zone.

-4. Low temperature process as defined in claim 3 in which the thirdvapor is warmed upon heat interchange with the compressed gaseousmixture, compressed and then added to the warm compressed gaseousmixture.

5. Low temperature process as defined in claim 4 in which vapor producedby partial evaporation of the first condensate is warmed by heatinterchange with compressed gaseous mixture, compressed and then addedto the warm compressed gaseous mixture.

6. Low temperature process as defined in claim 5 in which the fourthcondensate is vaporized upon heat interchange with compressed gaseousmixture, compressed, partly liquefied to provide a vapor portion and thevapor portion is fed to the fractionating zone.'

7. Low temperature process as defined in claim 6 in which the compressedgaseous mixture is passed in heat interchange with fourth condensateprior to separation of the gaseous mixture into the first vapor and thefirst condensate.

8. Low temperature process as defined in claim 7 in which the firstcomponent is hydrogen, the second component is carbon monoxide and thethird component is methane and in which the refrigerant is liquefiednitrogen under subatmospheric pressure.

References Cited UNITED STATES PATENTS 2,591,658 4/ 1952 Haringhuizen6223 3,020,723 2/ 1962 De Lury et a1 6-240 XR 3,095,294 6/ 1963 Knapp eta1 62-24- XR 3,107,992 10/1963 Sellmaier 6240 XR 3,224,207 12/1965 Feist62-40 XR 3,271,965 9/1966 Maher et al. 6240 XR 3,339,371 9/1967 Ichihara62-23 XR 3,370,435 2/ 1968 Arregger 6228 WILBUR L. BASCOMB, JR., PrimaryExaminer U.S. Cl. X.R. 62-26, 28, 31, 40

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo.3,508,4l3 Dated April 28, 1970 Inventor(s) J. A. PRYOR It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

r- 001. 4, line 17, "boil" should be coil Col. 6, line 19, "cylce"should be cycle Col. 6, line 25, "has" should be gas Col. 6, line 34,"steram" should be stream Col. 7, line 12, "exists" should be exits Col.8, line 49, "hours" should be hour YR SIGNED Mu SEALED (SEAL) Attest:

EdwardM-Fletchflrn m HUYLER goffim Ii LIME SQ comissioner of Patents

